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ENERGY SYSTEMS Energy from the food we eat is made available for use by the body’s cell through a molecule called ATP (Adenosine triphosphate). ATP is the body’s energy currency. ATP is made up of one adenosine and three phosphate molecules. The potential energy stored within an ATP molecule is used for all energy requiring processes within a cell. When ATP is split it releases energy that can be used for muscular contractions. ATP→ADP + P + energy Our cells only have enough ATP stored to last for a very short period of time (only a few seconds). Once this has been used more ATP needs to be produced. Fuel molecules from our foods can be broken down to provide energy which can be used to join adenosine diphosphate and phosphate to form adenosine triphosphate. ADP + P + energy from food fuels →ATP Our energy systems break down the food fuels to reproduce ATP. There are three energy systems at work in our body. These systems operate together however the extent to which one takes over depends on the intensity and duration of the activity. Energy in our body can be produced two ways Anaerobically - WITHOUT oxygen present. Aerobically - WITH oxygen present. Alactic or phosphogen system. This system uses the reserve fuel creatine phosphate which is stored in muscle fibres. ATP is broken down into ADP + P then resynthesized with the expense of the phosphate from the creatine phosphate molecule. The following reactions occur: ATP → ADP + P + energy (for cross bridging) CP →Cr + P + energy Energy (from CP above) + ADP + P → ATP Energy produced via the alactic system is utilised in activities of high intensity involving explosive movements of a short duration (up to 10 seconds), as our muscles only store a small amount of ATP and CP the duration of this system in limited. ATP and CP stores are replenished during recovery. If we continue to exercise beyond 10 seconds (Eg a longer sprint), we would utilise the lactic or glycolytic system. Fit College Energy Systems v1.1 Mar 2012 1 Lactic or Glycolytic System Carbohydrates are the main fuel used by this system which dominates in activities of maximal intensity and limited duration. Glycogen (form of carbohydrate stored in muscles) Glucose ADP + P 2 ATP Pyruvic acid Insufficient oxygen Lactic acid (by product of anaerobic glycolysis) This system is used in events lasting 2-3 minutes. The limiting factor of this system is the accumulation of lactic acid in the muscle causing it to fatigue. Aerobic System The aerobic system dominates during longer events and endurance activities. Remember that a person’s fitness level has a role in determining which system can override the others. The aerobic system is used in sub-maximal activities that are performed for long periods. The main fuels for this system are carbohydrate and fats. Glycogen (form of carbohydrate stored in muscles) ADP + P Glucose 2 ATP 36 ATP + Carbon dioxide + Water Pyruvic acid Sufficient oxygen NB – 38 molecules of ATP are produced from the breakdown of one glucose molecule Kreb cycle (this takes place in the mitochondria of the cell) Fit College Energy Systems v1.1 Mar 2012 2 Anaerobic Threshold This is the point where the body cannot supply oxygen to the working muscles as fast as it is needed so the body is required to supply more of its energy from the anaerobic system. This in turn causes the onset of blood lactate accumulation. The fitter the individual is, the longer it will take to reach the anaerobic threshold. Removal of Lactic acid from blood and muscle Lactic acid accumulates in the muscles during intense exercise, causing muscle fatigue and forcing the performer to stop exercise. The greater the effort, the more lactic acid will be accumulated. Lactic acid is removed from the blood and muscles during recovery, with the removal being faster when a light jog or warm down is performed. The lactic acid enters the blood stream and goes to the liver where it is converted back into glycogen. Skeletal muscles are also able to oxidise lactic acid to produce carbon dioxide, water and ATP and so continued activity will mean that greater amounts of lactic acid will be removed. Perceived Rate of Exertion (PRE) This can be used to assess the level of intensity a person is working at. Generally a scale of one to ten is used. The person is asked to identify where on the scale they are during a specific activity. One is the lowest intensity (e.g. very slow walking) while ten is the highest intensity (e.g. sprinting). The lower the PRE the longer the person should be able to maintain the activity. Steady state This occurs when the heart rate reaches the optimal level to meet the specific demands of the activity. The heart rate then remains steady. Maximal aerobic capacity During exercise the energy demands for our body increase. This causes a greater demand for oxygen. An increase in ventilation occurs in response to this. Heart rate and blood flow also increases. Maximal Oxygen Consumption or VO2 max is the maximal volume of oxygen consumed per minute during exercise. This is also the amount of oxygen capable of being transported and consumed by the working muscles. Two main factors determine VO2 max: The cardio respiratory system’s ability to take in and transport oxygen. The oxygen extraction capabilities of the muscle, e.g. the muscle’s ability to use the oxygen. Fit College Energy Systems v1.1 Mar 2012 3 Oxygen debt The difference between oxygen demand and oxygen consumed is called oxygen deficit. Once exercise ceases extra oxygen is still consumed to repay the oxygen deficit that occurs before steady state is reached. This is known as Excess Post Oxygen Consumption (EPOC). The extra oxygen is used for a number of tasks: To replenish oxygen reserves To convert lactic acid into pyruvic acid To replace glycogen stores To replenish creatine phosphate stores Re-oxygenation of venous blood. EPOC has two components – a fast component and a slow component Fast component: This is the initial component and utilizes up to 4 liters of oxygen. The main functions of this component are: Replenish myoglobin and haemoglobin stores. Restore ATP and CP stores to resting levels. Provide energy for increased ventilation and elevated heart rate. Slow component: This component may take hours or up to one day. It utilizes between 5-14 liters of oxygen. The main functions are: Convert lactic acid to pyruvic acid and glycogen. Replenish glycogen stores. Repair tissue damage. Fit College Energy Systems v1.1 Mar 2012 4